St. Hilarius may refer to:
Saints Hilarius or Hilary of Poitiers (c. 310–c. 367), Bishop of Poitiers and Doctor of the Church Pope Hilarius (died 468), Catholic pope and saint Hilarius or Hilary of Arles (c. 403–449), Bishop of Arles and saint
Other uses St. Hilarius Parish Church of Näfels, Näfels, Glarus Canton, Switzerland